When a rifle is fired, the barrel is observed to “whip” or flex, and the point of impact of the projectile varies depending on the position of the muzzle when the projectile exits. Best precision is achieved when factors are controlled to permit the projectile to exit when the barrel is at a stationary maximum excursion, so that minute variances in projectile exit time have a minimal effect on the point of impact. Such barrel harmonics are relatively predicable in free-float barrels used for precision shooting, typically with bolt actions. However, when gas systems used for self-loading rifles are connected to barrels, the barrel harmonics are greatly complicated, and it is accepted that such systems have inferior accuracy potential relative to other systems, even when optimized.
When a projectile leaves the muzzle of a barrel, the projectile is quickly overtaken by the high pressure gases exiting the muzzle behind the projectile. Therefore, as the projectile speeds away from the muzzle, propellant gases rush continuously past it so the projectile flies in a three dimensional envelope of gas. This effect continues for several feet until the supply of gas from the barrel ceases and the remaining gases slow down and dissipate into the surrounding atmosphere.
Certain mechanical conditions existing in a gas-operated firearm at the instant of discharge cause the muzzle of the barrel to move vertically or laterally after the projectile has cleared the muzzle. The lateral movement of the barrel modulates the column of gas as it leaves the muzzle. Since the velocity of the gas is higher than that of the projectile, the effect of this modulation is carried forward to the moving projectile as the gas passes it, thus influencing the point of impact of the projectile.
If the mechanical conditions of the firearm were the same for each shot fired, then the point of impact of the projectile would also be the same for each shot, and accuracy would not be impaired. However, mechanical conditions vary from shot to shot in a magazine fed, gas-operated firearm.
The majority of prior art gas systems consist of a gas block rigidly attached to the barrel, where the gas block incorporates an integral gas cylinder and a gas piston housed within the gas cylinder. There is also an orifice communicating with the bore of the barrel and the gas cylinder. When such a system is energized with high pressure gas from the bore of the barrel, the gas cylinder and the gas block receive an impulse in the direction of the muzzle which causes the muzzle to be displaced downward when the gas system is located on top of the barrel, and which causes the muzzle to be displaced upward when the gas system is located under the barrel. The degree of displacement of the muzzle is governed by the resistance to motion of the breech mechanism as the gas piston is driven rearward. When a full magazine is inserted into the firearm, the cartridges press against the underside of the breech mechanism, and the resistance to motion of the breech mechanism is high, decreasing with each shot as the magazine is emptied. Because of the principle of Newton's Third Law of Motion, the gas block receives a greater impulse when the magazine is full than it receives with an almost empty magazine.
Other factors that can cause the impulse received by the gas block to vary are when firing the firearm in a downhill or an uphill attitude, where the mass of the breech mechanism would be a factor.
Still another factor that can cause the impulse received by the gas block to vary is found in firearms of the M-1 Garand, M-14, or Ruger Mini-14 type. These firearms all employ the same type of rotating breech bolt. The breech bolt has a smooth polished underside on its left and a V-notch underside on its right. The purpose of the V-notch is to clear the right magazine lip when the breech bolt rotates to the locked position.
In a double column, two-position feed magazine, cartridges pushing against the V-notch underside of the breech bolt cause considerably more resistance to rotation during the unlocking of the breech bolt than cartridges pushing against the left underside of the breech bolt. This difference in resistance to rotation reflects back into the impulse applied to the gas block. Thus, as cartridges are fed from the magazine, the force they apply to the underside of the breech bolt increases or decreases as cartridges are fed from the right or the left of the magazine and then decreases overall as the magazine is emptied.
Yet another factor that can cause the impulse received by the gas block to vary is caused by variations in the powder charge in the cartridges and variations in the projectile diameter and weight.
From the above it can be seen that for every shot fired from a gas-operated, magazine fed firearm, the muzzle of its barrel receives a lateral impulse which is different for every shot fired. Therefore, the gases issuing from the muzzle send a “pneumatic message” to the projectile as the gases overtake the projectile. This is analogous to the carrier wave in an FM broadcast being modulated by an audio signal.
Bolt action single shot rifles with floating barrels are known for their superior accuracy because the muzzle of the barrel moves repeatably. The cartridge load can be fine tuned to enable the bullet to exit with the barrel in a stationary position at its extreme limit of motion. In contrast, the gas tubes and cylinders of gas-operated firearms resist the whipping, flexing action of the barrel in unpredictable ways, making the firearm less precise.
It is therefore an object of this invention to provide a gas operating system for fully and semiautomatic firearms which does not convey any impulses or other mechanical disturbances to the barrel of a firearm.